Theory:

Mridu had visited her cousins LalliRavi and Meena with her grandmother Tapi. When she entered their house, she noticed an old, dusty pair of chappals with scrawny toe-marks on it. Ravi drags her hurriedly to the backyard to show her the cat that they had saved earlier that morning. He described that the cat belonged to the Pallava dynasty, and he related it to the Rishi-cat statue he had seen in Mahabalipuram. He had named the cat Mahendra Pallava Poonai, or MP Poonaiin short. As they talked, they heard a "kreech" sound from the window and Ravi explained it was Lalli's off-pitched violin, which she was learning to play from the music-master.
 
Next, they heard a wailing sound from a beggar at the gate. The harassed Rukku Manni told him to go away because he had been coming every day. Meanwhile, the beggar groaned about the blisters on his soles due to the scorching heat on the tar road. Mridu remembered the chappals she had seen when she entered and asked Ravi whose it was. Ravi immediately decided to give it away to the beggar. The music-master came out and searched for his chappals. Rukku Manni suspected the curiously silent children and asked them. They confessed and got scolded by her for donating things that did not belong to them.
 
Rukku Manni got Gopu Mama's almost-new chappals and gave it to the music-master. Later she realized she had to answer Gopu Mama when he asked where his chappals were. It is understood that Rukku Manni also had done the same deed as Ravi, donating things that did not belong to her!